I ordered and installed both pre cat Oxygen sensors today.
The units I removed were 12 years and 98K miles old.
There were no CEL lights or poor running engine.
I just did it because they are not overly expensive, and I just had my
valve stem seals all replaced. I'm sure some oil has been burnt by my
BMW N62 engine. Some would say a waste of money, possibly so.
Either way you look at it, it's done deal.

I found great prices on exact Bosch brand, same part number on Amazon.
They were about a 100 dollars each.

I love my X5 and intend for it to last another 10 years.
That's 20 dollars a year for new sensors.

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2003 4.6is X5
2003 525it
2003 E53 X5 Standard shift